German writer and Nobel laureate Gunter Grass, whose recent poem criticizing Israel as a threat to global peace sparked widespread controversy, was admitted to hospital for a medical "investigation" earlier this week.

A spokesman at Asklepios Clinic in Hamburg said that the admission had been planned for some time but would not give any further details regarding Mr Grass's health.

Mr Grass's spokesperson said: "Mrs Grass took her husband to a Hamburg hospital to undergo a scheduled investigation", adding that he would be home again within days.

The 84-year-old author has been under great scrutiny over the past week. His most recent work, What Must Be Said, criticises Israel's stance towards Iran, Israel's nuclear capabilities and Germany's willingness to support Israel. The poem provoked dismay around the world.

Following Israeli Prime Minister Benjamin Netanyahu's outrage over the poem on Thursday, Israel's Interior Minister Eli Yishai said Mr Grass could no longer enter Israel. He noted: "If Gunter wants to spread his twisted and lying works, I suggest he does this from Iran, where he can find a supportive audience."